Nucleotide sequence within Tn3926 confirms this as a Tn21-like transposable element and provides evidence for the origin of the mer operon carried by plasmid pKLH2.

The DNA sequence of the resolvase gene, resolution sites, and the region between the transposition functions and the end of the mercury resistance operon of the bacterial transposon, Tn3926, is presented. The sequence of Tn3926 upstream of the resolution sites is homologous to that bordering the 11.2-kb insert of Tn21, supporting the idea that this insert transposed into a progenitor of Tn3926. This region of Tn3926 also shows 97.0% identity to the mercury-resistant determinant of the plasmid, pKLH2, suggesting that this plasmid once harbored a close relative of Tn3926. It is proposed that the mercury resistance operon of Tn3926 will have a structure very similar to that found on pKLH2.